Conventionally, as a drive mechanism for rotating a robot's wrist unit around the longitudinal axis of the forearm at the distal end of the forearm, there is known one having a hollow part for letting filaments such as cables for driving respective wrist axes of the wrist unit and filaments for peripheral equipment attached to the distal end of the forearm through (for example, see PTL 1).
This drive mechanism has a structure in which a ring-like output hypoid gear connected to the wrist unit is rotatably supported by a proximal end part of the forearm through a bearing coaxially with the longitudinal axis of the forearm, and an input hypoid gear engaged with the output hypoid gear is supported through a bearing so as to be rotatable around an axis line extending in a vertical direction, and a wrist driving motor for supplying rotating force to the input hypoid gear through a spur gear pair is installed so as to extend vertically below the forearm. This helps to secure enough space for the hollow part penetrating through the inside of the forearm in a direction of the longitudinal axis of the forearm, and also enables the wrist unit to be driven to rotate by high torque while reducing speed of rotation from the wrist driving motor in two stages of the spur gear pair and hypoid gear set.